Being a Blood Angels player, I would also advise taking Blood Angels. While they are very good at assault, I'm not sure that they are the best Marines at it. I think Space Wolves give them a good run for their money, at the least.
Both armies are really cool and have excellent fluff. Pick what's coolest.
Example: I loved the look of Space Marines. I knew that was the army I would play. Since my friends got me into it, they advised against regular SMs because they were so overused. They described Blood Angels as really good assault troops where "event he dreadnoughts have jump packs!" Well as it turns out, they don't, but they were still a wicked cool army that I always enjoy playing with. Mind you, my battle record isn't great, but I still love them (and screaming at my chaplain when he screws up, which is nearly all the time).
So choose something that you will like playing with win or lose.
__________________ Lord of Fluff and Blood Angels Herald of Nurgle "I wield my power with the Emperor's Authority. Those who would say that I am 'radical' merely have minds too small and impotent to realize all the weapons at their disposal. Do not question my methods on account of these so-called 'Puritans'." -Inquisitor Mathias Rosenadel |